Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity.

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What do “tachionic” neutrinos mean for QG?

Reading about the spectacular Opera claim, I`m (again ;-P) wondering if a confirmation of superliminous neutrinos could help settle some still open quantum gravity issues ...? In this post, Lumo ...
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74 views

Derivation of metric of space time with a point source in 2+1 dimension using ADM formalism

In "Quantum Gravity in 2+1 dimension" by S Carlip, Sec 3.1 (where the metric of a spacetime with a point source is derived, using the ADM formalism), equation 3.8 states that (this is the momentum ...
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965 views

What is the essence of BCFW recursion techniques?

I have recently briefly read about new methods as the Britto-Cachazo-Feng-Witten (BCFW) on-shell recursion method. Can anybody please tell me about the essence of it? What does it mean for the ...
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263 views

What does AdS/CFT have to say about quantum gravity in our world?

The Ads side of the AdS/CFT correspondence is a model of quantum gravity in 5 dimensional antidesitter space. What can it say about quantum gravity in our 4-spacetime dimensions? Or is it just a toy ...
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454 views

What are the theoretical explanations behind the “no-boundary condition” in cosmology?

In his book "The Grand Design" on page 167-173 Stephen Hawking explains how one can get rid of the so called "time zero issue", meaning by this the very special initial state needed for inflation to ...
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159 views

AdS to dS uplifting and its opposite

So as I understand it, localized structures in AdS can wick rotated to dS, the boundary has to be complixified as can be seen here. Also, uplifting is another technique that can be used to move from ...
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386 views

How do I quantize a classical field theory

I have not been able to find any information about this on the Internet. I am a middle-schooler, 14, who self-studies physics, and I know up to and including ODEs, and some of the calculus of ...
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291 views

Deriving the reduced Green's functions in Polchinski's volume 1

In equation 6.2.7, Polchinski defines his reduced Green's functions $G'$ on the 2-manifold to satisfy the equation, $$ \frac{-1}{2\pi \alpha '}\nabla ^2 G'(\sigma_1, \sigma_2) = ...
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117 views

Where and how is the entropy of a black hole stored?

Where and how is the entropy of a black hole stored? Is it around the horizon? Most of the entanglement entropy across the event horizon lies within Planck distances of it and are short lived. Is ...
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262 views

What is the mechanism for fast scrambling of information by black holes?

Sekino and Susskind have argued that black holes scramble information faster than any quantum field theory in this paper. What is the mechanism for such scrambling?
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192 views

Motivation for “discretized quantum state spaces”

I know that the title of the question is rather vague, so let me clarify what I mean. For a quantum system, the set of states has infinitely (even continuously) many extreme points, i.e. there are ...
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204 views

How is black hole complementarity derived from path integrals or string theory?

How is the black hole complementarity version of the holographic principle derived from path integrals and/or string theory? That has never been obvious to me. Can someone show me how to do it step by ...
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216 views

Can T-duality resolve spacelike singularities?

Schwarzschild singularities are described by the Kantowski-Sachs metric with a contracting S2. Of course, T-duality doesn't apply to S2. But what about a Kasner-type singularity with two contracting ...
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737 views

How could spacetime become discretised at the Planck scale?

I didn't have much luck getting a response to this question before so I have tried to reword and expand it a little: In early 2010 I attended this inaugural lecture by string theorist- Prof. ...
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286 views

What are the current (popular(ish)) approaches to modelling the quantum nature of spacetime at the Planck scale?

My guess at a list of them would be: spin foams, casual sets, non-commutative geometry, Machian theories, twistor theory or strings and membranes existing in some higher-dimensional geometry... ...
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155 views

What are the good introductory resources for M-theory towards AdS/CFT?

I see a list here with a section titled M-theory - http://www.superstringtheory.com/links/reviews.html In there these two look promising, http://arxiv.org/abs/hep-th/9607201 and ...
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508 views

Is spacetime an illusion?

In consistent histories, for gauge theories, can the projection operators used in the chains be not gauge invariant? In quantum gravity, for a projection operator to be gauge invariant means it has ...
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478 views

What is the motivation for assuming “Page” scrambling for Hawking radiation?

What is the motivation for assuming "Page" scrambling for Hawking radiation? Obviously, at the semiclassical level, we want the outgoing Hawking radiation to look thermal and mixed. However, surely ...
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218 views

Is the only diffeomorphism invariant anthropic principle the final anthropic principle?

Quantum gravity is a gauge theory with the gauge symmetry spacetime diffeomorphisms. Presumably the quantum state of our universe is invariant under spacetime diffeomorphisms, including timelike ...
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1k views

Physical laws prior the big bang (quantum fluctuations)

A theory among scientists says that quantum fluctuations caused the big bang and created the universe. This seems plausible to me. What I can't grasp yet is how a quantum fluctuation can even start ...
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209 views

Superspace as the Hilbert Space for Quantum Gravity

Let $\mathcal{A}$ be the Ashtekar connection. Since $^{(3)}g_{AB}=i\frac{\delta}{\delta\mathcal{A}^{AB}}$ (see R. Penrose, 2004: Road to Reality. Vintage Books, 1136 pp.), the Ashtekar connection, in ...
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69 views

Timelike Loop Spaces as Projective Null Twistor Spaces

Let $\mathcal{M}$ be a spacetime, and let $\Omega\mathcal{M}$ denote the loop space of the spacetime. My idea is that the set of all closed timelike curves of $\mathcal{M}$ forms the projective null ...
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Spaans, “On Quantum Contributions to Black Hole Growth”

This paper was posted to arxiv a couple of weeks ago: http://arxiv.org/abs/1309.1067 From the abstract: The effects of Wheeler's quantum foam on black hole growth are explored from an ...
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714 views

Is it possible that QM is just GR?

The more I learn about General Relativity, the more it seems like it isn't fully understood. It seems that before it's full consequences were exhaustively understood, not 10 years after its discovery, ...
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567 views

Does the Opera result hint to a discrete spacetime?

Could the Opera result be interpreted as some kind of hint to a discrete spacetime that is only seen for high enough energy neutrinos? I think I've read (some time ago) something like this in a ...
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603 views

Can we apply Schrodinger equation in Newton Gravitational potential and derive the deterministic Newton's gravitation as a special case of it

We know the solutions for wave functions of a an hydrogen atom, and the energy values as given by spectral analysis of radiation emitted by Hydrogen, confirms the possible energy states as predicted ...
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449 views

What is the smallest existing thing in theory and law?

What is the smallest existing thing in theory and law?
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Higgs-Boson/Graviton [duplicate]

The Higgs boson gives particles mass. And the graviton is the theoretical force-carrier of gravity. Gravity depends on mass. So if the Higgs Boson gives things mass, it therefore gives them gravity. ...
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2k views

How does gravity force get transmitted?

How does gravity force get transmitted? It is not transmitted by particles I guess. Because if it was, then its propagation speed would be limited by the speed of light. If it is not transmitted by ...
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855 views

Why is gravity weak at the quantum level?

Why is gravity stronger than other forces at the macroscopic level, yet weaker than other forces at the quantum level? Is there an explanation?
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321 views

Set theory, category theory, realism and the recent “reality of the wavefunction” papers

I will add a better phrased question here. Do we need to consider quantum foundations to form a quantum theory of gravity? The kind of foundational question I am thinking of is expressed in the ...
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621 views

What are the implications for quantum gravity if the LHC sees no higgs?

Following the news in serious "non-hype" physics blogs I`ve learnd that as things are now one needs a lot of patience and more data to learn what happens in the higgs sector. There are already a ...
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479 views

Introductions to discrete space-time

It's comparatively easy (cum grano salis) to grasp the following concepts: Euclidean space-time (continous space and continuous time) classical mechanics (discretely distributed matter in continous ...
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88 views

What predictions can a quantum gravity theory make?

Some of the major challenges that heralded the need for quantum mechanics we're explaining the photo-electric effect, the double-slit experiment, and electrons behavior in semi conductors. What are ...
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321 views

How do gravitons and curved space time work together? [duplicate]

I've heard two different descriptions of gravity, and I'm wondering how they work together. The first is Gravitons: "The three other known forces of nature are mediated by elementary particles: ...
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162 views

Is BRST ghost number conserved in quantum gravity?

Quantum gravity needs Faddeev-Popov ghosts. Feynman showed that. Take a black hole. Hawking pair production of ghost-antighost pair. One ghost falls into the hole and hits the singularity. The ghost ...
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208 views

Could strings be geons?

Is it possible that string theory strings are geons? This may be an overly speculative or naive question, but is there an obvious reason why not? Both strings and geons seem to have roughly the same ...
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297 views

Gravitational and gauge-gravitational anomalies in N=1 D=4 supergravity coupled to a SUSY gauge theory with chiral matter

When people talk about the first superstring revolution they often mention the miraculous cancellation of anomalies via the Green Schwarz mechanism. My question is whether such a string-theoretic ...
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635 views

What is known on violations of unitarity or locality?

Recently the amplituhedron become a hot topic. I realized that two of the central pillars that QFT is based on, unitarity and locality, are no longer playing an important part (due to gravitational ...
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175 views

Phys.org Spectral geometry to unite relativity and quantum mechanics, restate in laymens terms?

Lingua Franca links relativity and quantum theories with spectral geometry Could someone give me a short synopsis of this article in laymens terms? What implications does this have in the physics ...
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136 views

Will Randall-Sundrum extra dimension scenario become defunct if not supported by LHC?

The Randall-Sundrum extra dimension scenario had been one of the most extensively studied class of theories. This offered a solution to the hierarchy problem. However, if this picture is not supported ...
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Was Planck's constant $h$ the same when the Big Bang happened as it is today?

Was Planck's constant $h$ the same when the Big Bang happened as it is today? Planck's constant : $$h= 6.626068 × 10^{-34}\, m^2 kg / s,$$ $$E=n.h.\nu,$$ $$\epsilon=h.\nu$$
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272 views

Gravity and Planck scale

What is the connection between Planck's constant and gravity? Why is the Planck scale the natural scale for quantum gravity? I would have though the scale would be related to G, not h.
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691 views

Is string theory a quantum theory of gravity?

I have read that string theory predicts (or requires ?) the existence of gravitons. So, would that make it a quantum theory of gravity ? If so, I have also read that quantum gravity would allow us to ...
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67 views

How can Planck units be consistent with conflicting dimensions of mass?

I suspect I'm missing something obvious, but I'm coming up blank. I've gotten pretty comfortable with so-called natural units over the years: in doing quantum mechanics/QFT, it's common to set $c = ...
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202 views

Fundamental Constants in a theory of everything (TOE)

Do physicists ever expect to be able to derive the fundamental constants of nature from theory? For example, if string theory or some other theory unites the four forces, would the theory be ...
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235 views

Question on inflation as a phase transition

I have just finished watching the following video http://www.youtube.com/watch?v=beQ9fZ0jVdE where Laughlin, Gross and some students discuss e.g. about inflation. The following question is risen: Is ...
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123 views

Why are some extra dimension theories known as strongly coupled and others as weakly coupled?

I was looking at pdf file of the presentation of a conference talk. The speaker discusses two types of "mechanisms" for stabilizing the weak scale and calls them "weakly coupled" and "strongly ...
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159 views

Hilbert of quantum gravity: bulk $\otimes$ horizon

I was reading a paper dealing with the Hilbert of quantum gravity (or more precisely what should it look like considering what we know from QM and GR) ref: http://arxiv.org/abs/1205.2675 and the ...
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153 views

Canonical quantum gravity

I am looking for an introduction (textbook or paper, or if someone wouldn't mind writing a memo on it) to canonical quantum gravity, specifically the concept of minisuperspaces. I have been reading ...